Integration of pulmonary venous velocity patterns with transmitral flow patterns has improved the noninvasive assessment of left ventricular diastolic function, providing qualitative assessment of ventricular compliance, atrial systolic function and ventricular end-diastolic pressures. To improve mechanistic understanding of their fundamental physical and physiological basis, a previous numerical model of transmitral flow has recently been expanded to include active ventricular and atrial systolic function, a closed loop circulation including the right and left heart and pulmonary and systemic vessels, and a more realistic approximation of the ventricular diastolic pressure-volume curve. Four specific hypotheses will be pursued, chosen to refine the model while yielding important data of physiologic and clinical interest: 1) the pulmonary venous system near the left atrium is predominantly inertial in nature, with resistance much less than inertance; this information can be used to quantify instantaneous changes in atrial pressure from pulmonary venous velocity observations; 2) an exponentially shaped atrial diastolic pressure-volume curve is critically important to produce systolic blunting of pulmonary venous flow observed in significant left ventricular dysfunction and systolic reversal in severe mitral regurgitation; 3) mitral inertance varies by disease state, being reduced in low-flow states with limited mitral opening and abruptly increasing when the mitral valve is enlarged by percutaneous valvuloplasty; 4) the operating stiffness of the left ventricle can be quantified by the transmitral deceleration time. Methodology will involve a well developed Doppler-hemodynamic data acquisition system, placement of a dual-sensor, Millar catheter through the right upper pulmonary vein (intraoperative setting) or across the atrial septum (cath lab) to obtain high fidelity left atrial, ventricular and pulmonary venous pressure. Simultaneous transesophageal echocardiographic acquisitions of mitral valve and pulmonary venous pulsed Doppler data and transmitral and intrapulmonary vein color Doppler M-mode data will be stored digitally along with the pressure data and analyzed in a customized LabVIEW program to address the specific hypotheses above.